Method of forming a gypsum based product

Abstract

A method of forming a gypsum based product is disclosed. The method comprises the steps of: calcining a mixture of water and gypsum under conditions of raised temperature and pressure within a vessel to produce an alpha-hemihydrate slurry therein; passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with additional water to produce a settable slurry, which is arranged to set to form the gypsum based product.

The invention claimed is: 
     
       1. A method of forming a gypsum based product, the method comprising the steps of:
 calcining a mixture of water and gypsum under conditions of raised temperature and pressure within a vessel to produce an alpha-hemihydrate slurry therein; 
 passing the alpha-hemihydrate slurry from the vessel to a mixer, adding additional water to the mixer, mixing the alpha-hemihydrate slurry and additional water to produce a settable slurry, which is arranged to set to form the gypsum based product. 
 
     
     
       2. A method according to  claim 1  further comprising the step of reducing the water content of the alpha-hemihydrate slurry to provide a separate water stream from the alpha-hemihydrate slurry. 
     
     
       3. A method according to  claim 1 , wherein the calcination step comprises substantially filling the vessel with water and gypsum so that the vessel is substantially devoid of free space, such that the water produced during the calcination of gypsum is prevented from evaporating. 
     
     
       4. A method according  claim 1 , wherein the raised temperature comprises a temperature within the range 110° C. to 170° C. 
     
     
       5. A method according to  claim 1 , wherein the raised pressure comprises a pressure within the range 2 to 8 Bars. 
     
     
       6. A method according to  claim 1 , further comprising the step of cooling the alpha-hemihydrate slurry after the step of calcining the mixture of water and gypsum. 
     
     
       7. A method according to  claim 6 , wherein the alpha-hemihydrate slurry is cooled to a temperature less than 100° C. 
     
     
       8. A method according to  claim 6 , comprising the further step, after the step of cooling the alpha-hemihydrate slurry, of de-pressurizing the slurry. 
     
     
       9. A method according to  claim 8  further comprising circulating the separated water stream to preheat further gypsum before entering the vessel. 
     
     
       10. A method according to  claim 8 , wherein after the step of reducing the water content of the alpha-hemihydrate slurry, the water content of the alpha-hemihydrate slurry lies within a range of 1-10 wt %. 
     
     
       11. A method according to  claim 1 , further comprises the step of grinding the alpha-hemihydrate slurry to reduce the size of particulates therein. 
     
     
       12. A method according to  claim 1 , wherein the step of passing the alpha-hemihydrate slurry from the vessel to the mixer comprises the step of maintaining the temperature of the alpha-hemihydrate slurry at over 70° C. 
     
     
       13. A method according to  claim 1 , wherein the time taken for the alpha-hemihydrate slurry to pass from the vessel to the mixer is less than 120 minutes. 
     
     
       14. A method according to  claim 1 , further comprising adding water to the hemihydrate slurry. 
     
     
       15. A method according to  claim 14 , further comprising the addition of one or more additives to the hemihydrate slurry within the mixer. 
     
     
       16. A method according to  claim 1 , wherein the gypsum based product comprises a gypsum board. 
     
     
       17. A method of forming a gypsum based product, the method comprising the steps of:
 calcining a mixture of water and gypsum under conditions of raised temperature and pressure within a vessel to produce an alpha-hemihydrate slurry therein; 
 passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with additional water to produce a settable slurry, which is arranged to set to form the gypsum based product, wherein the alpha-hemihydrate slurry is passed from the vessel to the mixer without undergoing a drying stage.